Wireless power transmission is a technology which converts electrical energy into magnetic energy and transmits electric power without electric wires. Such a method transmits electric power based on electromotive force induced in a coil in a rod portion (e.g., battery) area, and this electromotive force is proportional to a magnetic flux interlinked with the coil. Therefore, the most important factor in determining transmission efficiency is to highly interlink magnetic flux produced by a coil in a power portion (e.g., charger) area with the coil in the rod portion (e.g., battery) area.
A transmitter using such wireless power transmission largely includes a coil, a ferrite, a variable capacitor, and the like. The ferrite is a substance which is largely used for wireless power transmission because it increases the size of a magnetic field and the inductance value of a coil.
The coil is used to induce the magnetic field while the ferrite is used to increase the size of the magnetic field. The variable capacitor is used to adjust a resonance in a drive frequency band by offsetting the inductance value of the coil.
Most ferrites used to increase the size of the magnetic field are fixed around the coil and thus the magnetic field has a fixed direction, as shown in FIGS. 1 and 2. Referring to FIG. 1, a ferrite 110 is fixed around a coil 120.
For a clear understanding, FIG. 2 is shown as a cross-sectional view taken along line I-I′ in FIG. 1. Referring to FIG. 2, the coil 120 is placed on a rod portion 130 and the ferrite 110 is airtightly located inside the coil 120. Accordingly, a magnetic field 201 is concentrated only over the ferrite 110.
In other words, such a method has good efficiency if the coil in the rod portion (battery) area is placed at a given position for charging the rod portion, but has deteriorated efficiency if the coil in the rod portion area deviates from the given position.